The invention relates to a semiconductor circuit having a drive circuit, having a load that is disposed between a supply voltage, and having a controllable semiconductor switching element for switching the load. The invention furthermore relates to a switch-mode power supply having such a semiconductor circuit.
The expression controllable semiconductor switching element should be regarded as meaning a controllable (load-break) switch that, in addition to its actual functionalityxe2x80x94namely the switching of currents and voltages, has additional functionalities, such as temperature protection and freewheeling protection. A controllable semiconductor switching element may contain, for example, a power transistorxe2x80x94for example a MOSFETxe2x80x94or an IGBT.
Controllable semiconductor switching elements have a load circuit and a control connection for driving the semiconductor switching element. To control these semiconductor switching elements, an additional supply voltage is generally required in addition to a supply voltage for the load circuit, with the control signal being derived from the additional supply voltage. Such a requirement applies, in particular, to those circuit applications in which a load voltage that is very much higher than the control voltage used. Circuit applications such as these, for example, switch-mode power supplies, power supplies, switch-mode regulators, and the like, are frequently operated directly from the mains voltage.
A switch-mode power supply is a regulated power supply unit that does not require any mains transformer at all. In a switch-mode power supply, the mains voltage is rectified directly, and is smoothed in an energy storage capacitor, so that a high DC voltage is available. A controllable switch xe2x80x9cchopsxe2x80x9d the DC voltage so that a periodic square-wave pulse sequence is produced, which is transformed in a transformer in accordance with the desired transformation ratio of the transformer windings, and is then rectified and filtered once again. The configuration and method of operation of such a switch-mode power supply are described, for example, in CoolSET, TDA 16822, xe2x80x9cOff-Line current mode controller with CoolMOS on boardxe2x80x9d, Datasheet, Version 1.0, April 2000, from Infineon Technologies AG, in particular, on page 4 of that document.
In switch-mode power supplies, the supply voltage for the drive circuit that drives the load-break switch can be produced, for example, by an additional primary transformer winding. The supply potential that is obtained from the additional primary transformer winding is then fed directly to the drive circuit. However, when not switched on, no supply potential can be tapped off on the additional primary transformer winding. Thus, when switching on a switch-mode power supply, it is necessary to ensure that the drive circuit is supplied with power immediately, in order to make it possible to drive the load-break switch appropriately. A starting circuit is used for such a purpose, which produces a starting charging current that is derived from the load voltage and initially builds up the supply voltage on a buffer capacitor. The energy for the first switching processes of the load-break switch is then drawn from the buffer capacitor until the supply voltage for the drive circuit of the switching-mode power supply is produced across the additional primary transformer winding.
Either a so-called start-up resistor or a current source in the form of a depletion MOSFET is typically used for the starting circuit. However, such a discrete configuration of a starting circuit is not a particularly cost-effective solution, particularly due to the additional space required for the starting circuit and the additional components.
Furthermore, the starting circuit produces undesirable power losses during operation of the switch-mode power supply in the situation where the starting current cannot be switched off after starting.
In addition to the discrete version of a starting circuit just described, an integrated solution also exists, using comparatively complex high-voltage technologies. In such an integrated version, the starting circuit, the drive circuit, and the load-break switch are formed monolithically on a single chip. One such circuit configuration is described, for example, in European Patent Application 0 585 788 B1, corresponding to U.S. Pat. No. 5,285,369 to Balakrishnan. The company Power Integrations markets the corresponding semiconductor circuits under the designations TOPSwitch and TinySwitch. However, because the drive circuit and the load-break switch are integrated monolithically, they cannot be optimized independently of one another, and such inability to optimize frequently leads to overdesign of the individual circuit elements and, hence, typically, to the load-break switch requiring a large area related to its switched-on resistance.
Furthermore, in many switch-mode power supplies and clocked power supplies, it is necessary to know the load current flowing through the load-break switch and its waveform precisely. For example, in quasi-resonant switch-mode power supplies, which are in the form of flyback converters, the time at which the load current is switched on, and, hence, the time at which the current through the primary winding of the transformer is switched on, is derived from the zero crossing of the load current in the secondary winding of the transformer. The derivation is done in a conventional manner by detecting the zero crossing of the drain-source voltage, from which the supply voltage for the drive circuit is obtained. In addition to the complexity for the additional transformer winding required for such a purpose, the drive circuit requires a corresponding additional detector input for an external additional circuit, which carries out the evaluation of the zero crossing. A quasi-resonant switch-mode power supply according to the prior art is marketed, for example, with the product designation TDA 4605 by the company Infineon Technologies AG, located in Munich, Germany.
A further requirement occurs, in particular, in safety-relevant applications of such semiconductor switching elements. In applications such as these, the voltage applied across the load-break switch must be evaluated. When the load-break switch is switched off, the load circuit voltage and any overvoltage across the load-break switch, or else any discrepancy in the load circuit voltage that is caused, for example, by oscillation or load chopping, can be derived therefrom. When the load-break switch is switched on, it can be checked for correct operation by evaluation of the voltage that is present across the load-break switch. Until now, an external or else integrated circuit that was produced specifically for such a check and that supplies the corresponding status information relating to the load circuit voltage, has been provided to determine the voltage that is present across the load-break switch. Until now, the load-break switch has not itself been configured to supply status information relating to the load current or to the voltage that is dropped across the load path of such a switch.
The provision of a starting circuit, which is intended specifically for starting a generic type of such a semiconductor circuit, of an additional circuit that is intended specifically for detecting the zero crossing of the load current, and of an evaluation circuit that is intended specifically for evaluating the load circuit voltage that is dropped across the load-break switch, is, furthermore complex and, hence, makes the overall circuit configuration very expensive.
It is accordingly an object of the invention to provide a semiconductor circuit and a switch-mode power supply having such a semiconductor circuit that overcomes the hereinafore mentioned disadvantages of the heretofore-known devices of this general type and that at least partially satisfies the above requirements and that furthermore can be produced very much more easily in terms of its circuitry.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a semiconductor circuit including a drive circuit having a drive circuit output and producing a control signal at the drive circuit output, a controllable, integrated semiconductor switching element configured to switch itself on and off, a load-break switch for clocked switching of a load, the load-break switch having first and second load path connections, a control connection connected to the drive circuit output, and the control signal controlling the load-break switch through the control connection, a first current source having a first output and providing a starting charging current at the first output when the load-break switch is switched off, the first current source connected to the first load path connection, a monitoring device having at least one second current source with a second output, the second current source producing a status signal at the second output, the monitoring device measuring a voltage between the first and second load path connections and/or measuring a potential present at one of the first and second load path connections, the monitoring device producing the status signal dependent upon the voltage and/or the potential, and a starting charging device connected to the drive circuit and supplying the drive circuit with power through the starting charging current.
The semiconductor circuit according to the invention has a controllable, preferably clocked, semiconductor switching element with a load-break switch and a drive circuit that drives the load-break switch. In addition to standard connections for controlling the load-break switch (gate) and two load connections (drain, source), the semiconductor switching element also has further connections that, to a certain extent, upgrade the semiconductor switching element to an xe2x80x9cintelligentxe2x80x9d semiconductor switch, which provides a number of additional functions for operation of the semiconductor circuit. These additional connections include a connection for the starting of the semiconductor circuit, a connection for controlling the starting process, and a connection for providing status information, for example, about the load current and the load circuit voltage. The semiconductor switching element is upgraded, according to the invention, by an appropriate circuit to form a clocked semiconductor switch, which switches itself on and off.
The semiconductor switching element according to the invention also has a starting device and/or a monitoring device in addition to its conventional functionality. The drive circuit, and, hence, also the semiconductor switching element, can be switched on through the starting device, while they can be switched off, or can be kept in a switched-on state, through the monitoring device. Depending on the configuration, the monitoring device is used for short-circuit identification and/or to provide a facility for switching on or off in the event of an overvoltage. Such use allows the load circuit and the supply circuit to be optimally decoupled, that is to say, the circuit with the high voltage and the circuit with the low voltage.
The functionalities contained in the semiconductor switching element according to the invention can now be configured such that they can be used for the semiconductor circuit to switch itself on, for clocked control of the supply voltage for the drive circuit, to prevent the drive circuit from switching itself on, to switch the drive circuit and/or the load-break switch off in the event of defects, and for evaluation of the voltage that is dropped across the load-break switch and the control signals that are derived from such a voltage.
In accordance with another feature of the invention, the starting charging device includes the first current source and an energy storage capacitor charged by the starting charging current and, in a charged state of the capacitor, the capacitor supplying the drive circuit with a supply potential.
In accordance with a further feature of the invention, there is provided a decoupling diode disposed in series between the first current source and the energy storage capacitor and a voltage limiter disposed in parallel with the energy storage capacitor.
In accordance with an added feature of the invention, the first current source is a controllable current source.
In accordance with an additional feature of the invention, the controllable current source is a controllable semiconductor switch.
In accordance with yet another feature of the invention, the starting charging device has a switching-off device for switching off the starting charging device, the first current source has a control connection, the switching-off device has an input connected to a floating potential and an output connected to the control connection of the first current source, and the switching-off device switches, preferably, always switches, the starting charging device to a switched-off state whenever a potential at the input corresponds to a potential at the first output and/or a potential at the second load path connection.
In accordance with yet a further feature of the invention, there is provided a controllable switch and/or a limiter circuit disposed between the first output and the input of the switching-off device.
In accordance with yet an added feature of the invention, there is provided a zener diode, a limiter switch, and/or an integrated circuit disposed between the first output and the input of the switching-off device, at least one having a rising reverse current as temperatures rises and/or a reducing internal resistance as temperatures rises.
In accordance with yet an additional feature of the invention, the starting charging device has a detector device and a further output, the detector device produces a status signal at the further output at a zero crossing of a voltage dropped across the load-break switch and/or a potential present at one of the first and second load path connections, and the status signal switches the load-break switch to a switched-on state at each zero crossing.
In accordance with again another feature of the invention, the monitoring device has an overvoltage switch-on facility identifying when overvoltages are present across the load-break switch and switching on the load-break switch when an overvoltage occurs.
In accordance with again a further feature of the invention, there is provided an AND gate connected upstream of the control connection of the load-break switch with respect to a control signal flow direction, the monitoring device producing a switch-on signal in response to switching on in an event of an overvoltage, the switch-on signal being fed to the AND gate, and the AND gate switching on the load-break switch.
In accordance with again an added feature of the invention, the monitoring device has an undervoltage switch-off facility identifying undervoltages present across the load-break switch and, in an event of an undervoltage, switching off the load-break switch and/or not switching the load-break switch on.
In accordance with again an additional feature of the invention, the monitoring device has a hold circuit when switching off occurs in response to an undervoltage, the hold circuit has an inverter disposed between the second output and the control connection of the load-break switch, and an AND gate is connected downstream from the inverter and switches off the load-break switch for as long as the undervoltage is present.
In accordance with still another feature of the invention, there is provided a clocked drive signal controlling the semiconductor switching element.
In accordance with still a further feature of the invention, the load-break switch is a power semiconductor component, in particular, based on the compensation principle.
In accordance with still an added feature of the invention, the load-break switch is a power MOSFET and/or an IGBT.
In accordance with still an additional feature of the invention, the semiconductor switching element is in cell form and includes a plurality of cells having load paths, the load paths of a majority of the cells are connected in parallel and form the load-break switch, the starting charging device and/or the monitoring device have transistors, and a remainder of the cells form the transistors.
In accordance with another feature of the invention, the semiconductor switching element has a current measurement device having at least one cell of the power semiconductor component and measures the status signal through the load-break switch in accordance with a ratio of measurement cells to main cells.
In accordance with a further feature of the invention, the drive circuit has an oscillator having an output side, a logic circuit having an output side, and a driver circuit having driver circuit inputs, a supply potential is supplied to each of the oscillator, the logic circuit, and the driver circuit, the output side of the oscillator and the output side of the logic circuit are connected to a respective one of the driver circuit inputs, the driver circuit is connected to the control connection of the load-break switch, and the driver circuit is driven based upon a control signal, an oscillator signal, and/or a signal derived from the status signal.
With the objects of the invention in view, there is also provided a switch-mode power supply including a load, a semiconductor circuit having a drive circuit having a control signal input and a drive circuit output and producing a control signal at the drive circuit output, a controllable, integrated semiconductor switching element configured to switch itself on and off, a load-break switch for clocked switching of the load, the load-break switch having first and second load path connections, a control connection connected to the drive circuit output, and the control signal controlling the load-break switch through the control connection, a first current source having a first output and providing a starting charging current at the first output when the load-break switch is switched off, the first current source connected to the first load path connection, a monitoring device having at least one second current source with a second output, the at least one second current source producing a status signal at the second output, the monitoring device measuring a voltage between the first and second load path connections and/or measuring a potential present at one of the first and second load path connections, the monitoring device producing the status signal dependent upon the voltage and/or the potential, and a starting charging device connected to the drive circuit and supplying the drive circuit with power through the starting charging current, a transformer having a primary winding and a secondary winding with a secondary output, the semiconductor switching element configured to apply a substantially rectified voltage in a clocked manner to the primary winding, the secondary winding supplying power from the primary winding at the secondary output to the load, a feedback device connected to the control signal input, and the feedback device supplying one of a voltage produced at the secondary output and a current at the secondary output to the control signal input.
In accordance with an added feature of the invention, the drive circuit and parts of the starting charging device not contained in the semiconductor switching element are integrated together on a single semiconductor chip.
In accordance with yet a further feature of the invention, the semiconductor switching element is integrated on a first semiconductor chip, the drive circuit is integrated on a second semiconductor chip, and the first and second semiconductor chips are embedded together in a single housing for a semiconductor component.
In accordance with an additional feature of the invention, the switch-mode power supply is a flyback converter.
In accordance with yet another feature of the invention, the switch-mode power supply is a forward converter.
In accordance with a concomitant feature of the invention, the switch-mode power supply is a quasi-resonant switch-mode power supply.
In complete contrast to circuit configurations according to the prior art, in which at least some of these functionalities are carried out by a circuit configuration that is provided specifically for such a purpose, that must be connected to the semiconductor switching element form the outside, and that is, thus, very complex and expensive, the semiconductor circuit according to the invention can be provided by integration of all the prior art functionalities by a single semiconductor switching element and a drive circuit that is specifically intended and optimized for such a purpose.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor circuit and a switch-mode power supply, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.